An internal combustion engine may include direct fuel injectors for supplying fuel directly to engine cylinders. The direct fuel injectors may be sized so that they may accurately provide either small or large amounts of fuel to a cylinder during a cycle of the cylinder. However, to provide large amounts of fuel to the cylinder to meet driver demand torque, the direct fuel injectors may have to begin injecting fuel before intake valves of the cylinder close so that a desired amount of fuel may be injected to the cylinder. If intake manifold pressure is sampled long before the cylinder's intake valve closes, the intake manifold pressure may not be indicative of air charge in the cylinder, especially during engine starting when intake manifold pressure changes significantly in a short period of time. Consequently, basing an amount of fuel injected to a cylinder solely off of intake manifold pressure before intake valve closing of the cylinder may yield an air-fuel ratio in the cylinder that deviates from a desired air-fuel ratio of the cylinder. Further, spark timing for the cylinder may deviate from desired spark timing due to errors in the cylinder air charge estimate.
The inventors herein have recognized the above-mentioned issues and have developed an engine operating method, comprising: injecting a first amount of fuel to a cylinder during the cycle of the cylinder in response to an open loop estimate of cylinder air charge, the open loop estimate of cylinder air charge a function of a first cylinder to fire since a most recent engine stop and an actual total number of combustion events since the most recent engine stop.
By adjusting a cylinder air charge estimate as a function of the first cylinder to fire since a most recent engine stop and an actual total number of combustion events since the most recent engine stop, it may be possible to provide the technical result of improving engine air-fuel control. In particular, the inventors herein have recognized that an observation of cylinder air charge from a previous engine start may be the basis for changing a cylinder air charge estimate for a present engine start. A cylinder air charge estimate that is determined during a prior engine start and that is based on pressure in a cylinder corresponding to a particular first cylinder to fire and an actual total number of combustion events since a most recent engine stop may be the basis for updating a cylinder air charge estimate that is based on engine intake manifold pressure during a present engine start. A cylinder air charge estimate that is determined in a present engine start and that is based on cylinder pressure may provide a cylinder air charge estimate that includes effects of intake manifold air flow characteristics and cylinder head air flow characteristics during engine starting. The cylinder air charge estimate determined during a previous engine start and that is based on cylinder pressure may also be the basis for adjusting a cylinder air charge estimate that is based on intake manifold pressure for a present engine start. The cylinder air charge estimate determined during a previous engine start may modify the cylinder air charge estimate that is based on intake manifold pressure during the present engine start for the effects of intake manifold air flow characteristics and cylinder head air flow characteristics. In this way, the cylinder air charge estimate that is based on intake manifold pressure and that is determined during a present engine start may be adjusted closer to the actual amount of air in a cylinder for the present engine start. Therefore, fuel injection may be initiated earlier in a cylinder cycle based on an improved cylinder air charge estimate so that a desired amount of fuel may be injected during the cylinder cycle.
The present description may provide several advantages. Specifically, the approach may provide improved engine air-fuel ratio control. Further, the approach may provide for more repeatable engine starting. Further still, the approach may improve engine starting no matter which engine cylinder is first to fire after a most recent engine stop.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.